As a device for measuring an inner diameter of a cylindrical member on non-contact basis, a non-contact type inner diameter measuring device is known, by which a laser beam is projected in a total circumferential direction, and an optical ring is formed on an inner surface of the cylindrical member, and an image of the optical ring is picked up, and a shape and a diameter of the optical ring are measured from the image thus picked up.
Each of the Patent Document 1 and the Patent Document 2 discloses a non-contact type inner diameter measuring device, which projects a laser beam in a total circumferential direction and picks up an optical ring formed on the inner surface of the cylindrical member and measures the shape and the diameter of the optical ring from the image. In the inner diameter measuring device disclosed in each of the Patent Document 1 and the Patent Document 2, a cone mirror with a conical reflection surface is used as means for projecting a laser beam in a total circumferential direction, and by projecting the laser beam to a vertex of the cone mirror, the laser beam is reflected in a total circumferential direction. The laser beam diffused in a total circumferential direction is projected to the inner surface of the cylindrical member, and an optical ring is formed. This optical ring is picked up by an image pickup device, and a diameter, a shape, etc. of the inner surface are measured from an image acquired.
However, there are cases where various types of irregularities are existed on the inner surface of the cylindrical member such as a graded step protruding vertically from the inner surface, a curved portion protruding while being curved, a tapered part protruding in tapered manner, etc. By the conventional type inner diameter measuring device, it has been difficult to measure the diameter, the shape, etc. of the inner surface, in the graded step, the curved surface or the tapered part.
To solve the problems as described above, it is an object of the present invention to provide an inner diameter measuring device, which projects a laser beam in a total circumferential direction by means of a cone mirror, forms an optical ring on an inner surface of a cylindrical member, and measures an inner diameter and a shape of the cylindrical member based on the optical ring, wherein the inner diameter measuring device enables to measure even when the cylindrical member has irregularities on the inner surface.